You may well say that CGPM seems like a weird abbreviation of General Conference on Weights and Measures and you would be right. Until you consider that, amazingly, English is not the only language in the world and that CGPM actually is an abbreviation of Conference Generale des poids et mesures (apologies for leaving out the accents) Yes, it is French! And the main language their reports are written in is French! Which is probably why the British (or more specifically the English) are so resistant to using the completely sensible and rational units like metres and grams. You know, because it all smells a bit garlicky. And what could be more useful than a system based on how heavy a stone is and how many pounds with a hammer it takes to break up a stone (this is definitely where the unit ‘pound’ comes from)
You probably know full well that the conversion rate between calories and joules is one calorie is equal to 4.2 joules.
And those things on packaging that we call calories? They aren’t actually calories, they’re kilocalories (kcal) and 1 kcal is equal to 4.2kilojoules(kJ).
Which all seems very confusing.
Why did the poor calorie lose out to the joule in the battle to be the standard international unit?
Well, the calorie was first defined by the French chemist Nicolas Clement. He defined it as the amount of energy required to heat 1kg of water by 1 degree C.
Fact fans will know that the joule is defined as the energy required to raise 1 gram of water by 0.24 Kelvin. The Kelvin is another of those SI units. 1 Kelvin is basically the same as 1 degree Celsius
So, 1kJ will raise 1kg of water by 0.24K. Or 4.2kJ will raise the temperature of 1kg of water by 1 degree C.
Hope that’s all clear. As mud.
So, I hear you shout, the calorie that Nicolas Clement defined was actually what we now call a kilocalorie?
That is correct.
Along comes Mr Joule at this point.
Now, I always assumed that Joule was French and that the reason that we used joules as a standard unit was because the French are in charge of the standard unit system, what with their insistence on the very sensible metres, grams, Pascals, amperes and what not. So obviously they were going to lever in their man, Monsieur Joule. After all, they let us have the Kelvin, but probably only after a lot of shrugging and sucking of teeth.
James Prescott Joule, born and bred in Manchester, developed his theories to help him make beer in a more cost effective way.
There had been a theory, called the CALORIC theory, which proposed that heat was a sort of fluid called CALORIC which flowed from hot objects to cold objects. One of the keystones of caloric theory was that heat, because it was made of caloric fluid, could not be created or destroyed. There was so much caloric fluid in the universe and if one thing got hotter, something else would have to get colder. Various experiments and theorists, for example Sir Benjamin Thompson, Count Rumford, suggested that this was not the case…
In the manufacture of cannons, when the interior of the cannon is ‘bored’ to make it smoother, the friction generates heat, said Count Rumford. This boring could be done repeatedly and the cannon would get hot. Heat was being generated, therefore heat was being created. Caloric theory was wrong. Though lots of people said his experiment was rubbish and, ho ho ho, a bit boring. Snigger.
Anyway, James Joule performed a series of experiments which showed that heat was generated within an electric conductor and not transferred from another part of his equipment. He also published experiments that showed that a mechanical movement, like a falling weight, could be used to generate heat. All of this was leading up to a theory that different types of energy like heat and movement were interchangeable and could be transformed from one to another. This eventually became the First Law of Thermodynamics which states that the total energy of an isolated system is constant; energy can be transformed from one form to another but cannot be created or destroyed.
And so, because James Joule’s work led to an overarching view of energy, he got the standard unit for energy named after him, and Nicolas Clement didn’t get the calorie to be renamed in his honour. This is why I am not counting Clementines.
Also, it probably helped a bit that a British committee got to pick the name for the unit of energy and so they went for the Mancunian rather than the Frenchie. No bias whatsoever.